The subject matter of this application is related to the subject matter of U.S. patent application Ser. No. 09/754,595 filed on even date herewith by Shallow et al. entitled xe2x80x9cMethod And Apparatuses For Electrochemically Treating An Article.xe2x80x9d
1. Technical Field
This invention relates to a method for electrochemically processing articles, such as cylindrically shaped, hollow tubing articles, and more specifically, to methods and to apparatuses used for plating processes.
2. Background Information
One example of hollow articles requiring plating is tubing used in the aerospace field. The tubing is used for flowing fuel, lubricating fluid, hydraulic fluid and the like, typically in high-pressure applications. The tubing is relatively small in diameter (less than one inch) and is typically joined to a mating component using braze material. The tubing frequently receives a coating to provide a smooth surface. The coating is carefully applied because the coated tubing has controlled tolerances. The smooth surface and controlled tolerances ensure that capillary forces will urge the braze material to flow into a predetermined gap between the tubing and the component.
One approach for providing the coating uses a plating process having a large-scale bath and includes disposing many pieces of tubing in the bath. A large-scale plating bath may not efficiently use the plating solutions, increasing purchasing costs and increasing disposal costs of the environmentally sensitive waste. Depending on the location of the tubing in the bath, the tubing might receive a thicker than desired coating or a thinner than desired coating. In addition, a large-scale plating bath may well be located at a site remote from the location at which the brazing processes are carried out.
Another approach for providing the coating is a brush plating process. The electrolytes used for brush plating have a higher metal content than electrolytes for conventional plating baths. Brush plating processes employ a carbon anode wrapped in a conductive pad. The conductive pad is soaked in the electrolyte. This is essential to achieve higher rates of plating deposition. A current is passed through the pad and to the article as the operator rubs the pad over the surface.
An advantage of the brush plating process is little waste and acceptable levels of time for work in process. However the process is labor-intensive and variations in technique from operator to operator increase the difficulty of precisely controlling the plating thickness. In addition, the operator must handle harsh chemicals during cleaning and etching and must hold and move the anode with a repetitive motion that causes fatigue and which might cause repetitive motion injuries.
Accordingly, scientists and engineers working under the direction of Applicants Assignee have sought to develop a plating process and apparatus for use with such processes that provide efficient use of solutions, efficient use of rinsing water and may be installed in local work areas.
This invention is predicated in part on the recognition that using concentrated solutions of the type having higher metal content for use with high-speed plating may advantageously be used in local work areas by using dedicated plating cells. It is also predicated on recognizing that dedicated cells may be provided with flow patterns that promote rinsing processes and electrochemical processes associated with plating. Is also predicated on, in one embodiment, recognizing that such dedicated cells promote automation of the plating process. In this context, electrochemical processes refer to process steps for an article, such as etching, activating and electroplating and other steps that pass a current through an electrolyte. The current is passed between a pair of electrodes where the article acts as one of the electrodes, whether as an anode or a cathode. Rinsing refers to those steps using an apparatus to prepare the surface by removing contaminants from the surface with a rinse fluid, such as by removing electrolyte from the surface with rinse water.
According to the present invention, a method for electrochemically plating an article which requires at least two preparatory process steps and a plating process step includes the step of providing an array of cells which includes electrochemical cells, each electrochemical cell being dedicated to and containing during a step the necessary solutions for carrying out the step in the plating process, each electrochemical cell having a first dedicated electrode formed by an electrode attached to the cell and being of a size and having an interior for receiving a volume of fluid connected with that step which is appropriate for carrying out the process step on a single article at that cell; the step of adding to the cell a second dedicated electrode formed by the article; and, further includes the step of moving articles relative to the cells such that a single article moves in sequential fashion through the dedicated cells.
In accordance with one embodiment, the method includes flowing a volume of solution for performing the process step through the electrode of at least one of the dedicated cells.
In accordance with one detailed embodiment, the method includes moving an array of tubings sequentially through the dedicated cells such that a single tubing is at each cell as the process steps are being performed and wherein the duration of time at any dedicated cell is at least equal to the duration of time at that one dedicated cell requiring the longest amount of time for carrying out the process.
In accordance with one detailed embodiment, the method includes indexing the tubings of an array of tubings, each to an associated cell; moving the array of tubings with respect to the cells, each into an associated dedicated cell; performing the process step at the dedicated cell; removing the array of tubings from the dedicated cells; and, reindexing the tubings with respect the cells by moving the array of tubings together, each to the next dedicated cell, and further includes removing from the array of tubings, the tubing which has completed processing and adding a tubing to the array for beginning the method.
In one detailed embodiment, the method includes moving the tubing in sequential fashion through dedicated cells for performing the steps of electrochemical cleaning using an electrolytic fluid, rinsing using water, electrochemical etching using an electrolytic fluid, rinsing using water; electrochemical activating using an electrolytic fluid; electroplating using an electroplating solution, and, rinsing using water.
In one particular embodiment, the electrochemical cleaning solution is a base; the etching solution is an acid; the activating solution is sulfuric acid and ammonium sulfate; and the electroplating solution is a nickel plate solution.
In one detailed embodiment, the method includes using a data processing device to determine the duration of time that a tubing spends at a dedicated cell, which includes determining the amp-hours consumed, the volume of rinse fluid consumed between dedicated electrochemical cells; and determining the dedicated cell and tubing requiring the longest time and turning off the flow of fluid and current to the other cells as appropriate once the process step being performed at a dedicated cell is complete.
According to the present method, the step of rinsing a tubing includes disposing the tubing in a chamber having passages directed toward the chamber and further includes a guide member extending axially in chamber, the method further including the steps of sliding the tubing over the guide member; flowing a rinse fluid longitudinally through the guide member and radially outward through the guide member such that the fluid impinges on the interior of the tubing while simultaneously flowing fluid through the passages in the wall that are directed toward the tubing disposed in the center of the chamber under significant pressure, such as a pressure which is in excess of ten pounds per square inch gauge (10 psig) and in some applications is equal to fifteen pounds per square inch gauge (15 psig).
In accordance with the present invention, the step of flowing a rinse fluid includes the steps of detecting the presence of the tubing in the chamber; flowing a predetermined amount of rinse fluid to the chamber prior to flowing the rinse fluid through the pin and through the walls the chamber.
A primary feature of the present invention is a method which uses dedicated electrochemical processing cells in a plating process. In one embodiment, a feature is indexing and reindexing an array of articles with respect to the dedicated cells as the processes are performed in each cell. Another feature is forming a cell such that a first electrode forms at least a portion of electrode chamber within the cell. Another feature is disposing the article being processed in the electrode chamber to form to the second electrode. Still another feature is flowing electrolytic fluid through the electrode chamber under operative conditions. Still another feature is forming dedicated rinsing cells having passages for impinging rinse fluid against the article. Still another feature is a rinsing cell having a guide member which both positions the article in the rinsing cell and flows rinse fluid to the interior of the article to rinse away electrolytic fluid.
A primary advantage of the present invention is the efficiency of the process which results from using dedicated cells having small volumes of fluid for repetitively performing a plating operation that reduce waste and purchasing costs. Another advantage is the ability to use such cells in a small, local area. An advantage of the method is the convenience of having a plating apparatus in close proximity to an area which performs brazing. Another advantage is the efficiency that results from using the dedicated cells with devices that facilitate automation of the process.
The foregoing features and advantages of the present invention will become more apparent in light of the following detailed description of the best mode for carrying out the invention and accompanying drawings.